Many different designs have been made over the years for rolling piston or rolling rotor motors and pumps, but these have the commercial drawback of a mechanical rubbing seal at the periphery of the rolling piston. The seal wears with use, thereby limiting the life of the apparatus and necessitating a tear down for seal replacement.
There is a commercial need for a rotary piston or rolling rotor machine wherein the seal is absent or is out of contact with the main rotor or piston so that there is freedom from frequent seal replacement.